Wednesday, February 21, 2007

Integral View of Sky

Credits: IBIS survey team

Integral expands our view of the gamma-ray sky
The upper image shows the sky distribution of four of the main soft gamma-ray source populations observed in the third Integral/IBIS survey catalogue. This newly-released catalogue contains 421 sources. Of the known systems, the low-mass X-ray binaries (LMXB) are old systems mainly populating the galactic bulge, the high-mass X-ray binaries (HMXB) are younger systems seen along the galactic plane, and the active galactic nuclei (AGN) are extragalactic sources seen over the whole sky. Around one out of four of the sources seen by Integral are unidentified, and their distribution is also shown.

The lower picture is a false colour image of the central region of our galaxy. This is a composite image based on all-sky IBIS/ISGRI maps in three energy windows (between 17 and 100 keV) and represents the true 'X-ray colours' of the sources. Red sources are dominated by emission below 30 keV, while blue sources have harder spectra, emitting strongly above 40 keV.

One of the most remarkable "relic" gamma-ray clouds of the new catalog, the source HESS J1825-137 which is 100 light-years across. The zoomed box shows the much smaller X-ray nebula (data from the XMM-Newton satellite), surrounding the middle-aged (21000 years old) pulsar PSR B1823-13. (Credit: Astroparticule et Cosmologie (APC), CNRS)

High-Energy 'Relic' Wind Reveals Past Behavior Of Dead Stars
Winds from pulsars have been known for many years. The most famous example is that from the pulsar in the center of the Crab Nebula, a bright cloud of expanding gas from a star that exploded in the year 1054. In that case, the wind generates X-rays (which have less energy than gamma rays) through synchrotron radiation and gamma rays through the inverse Compton scattering. These X-rays and gamma rays are seen coming from gas a few light years across at most.

The objects detected by the H.E.S.S. team are far more extended. The glow of gamma rays seen from the pulsar PSR B1823-13, for example, is approximately 100 light years across. A light year is the distance a particle of light, traveling 186,000 miles per second travels in one year.

The larger size of this gamma-ray emitting region means the electrons producing the gamma rays have traveled further and so come from a period earlier in the pulsar’s history. This in turn means that studying the gamma rays from pulsar winds can give astronomers insight into the history of the pulsar itself and how its magnetic field has changed over the past tens of thousands of years.

Powerful Solar Winds colliding head-on from Universe Today
NASA Scientists Find High Energy Systems Hidden in 'Gas Cocoon'
First X-Ray detection of a Colliding Wind Binary from Science Daily

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